Pseudoolenoides acicaudus Hintze, 1953

Adrain, Jonathan M. & Karim, Talia S., 2012, 3467, Zootaxa 3467, pp. 1-97 : 25-29

Pseudoolenoides acicaudus Hintze, 1953

Plate 16, figs 1–23, Plates 17–19

1953 Pseudoolenoides acicaudus Hintze , p. 229, pl. 27, figs 7–11.

1973b Pseudoolenoides acicaudus Hintze ; Hintze, text-fig. 28.

non 1974 Pseudoolenoides acicaudus Hintze ; Shaw, p. 22, pl. 1, figs 13–22, 24 (= Pseudoolenoides oilcreekensis n. sp.).

1991 Pseudoolenoides acicaudus Hintze ; Ross and Ethington, p. 158.

1991 Pseudoolenoides acicaudus Hintze ; Church, fig. 2.

1996 Pseudoolenoides acicaudus Hintze ; Fortey and Droser, p. 87.

Material. Holotype, pygidium, AMNH-FI 26497 , and paratype AMNH-FI 26496 from Section CP 45.7 m, and assigned specimens SUI 130038–130060 from Section CP 48.8 m, Kanosh Formation (Dapingian; Pseudoolenoides acicaudus Zone ), Crystal Peak Hills , Ibex area, Millard County, western Utah, USA.

Diagnosis. Librigena with very narrow field with very subdued transverse raised line arc; librigenal posterior border with prominent posterior point at contact with facial suture; pygidium with five unreleased segments.

Description. Cranidial measurements were made on the most complete specimens of Pl. 16–17. Measurements were doubled from the sagittal line when necessary, e.g., for specimens with a single intact palpebral lobe. Cranidium broad and fairly long, moderately vaulted (sag., tr.), widest across palpebral lobes (δ), 136.2% (130.4–144.3%) sagittal length, consistently wide posteriorly, with width across β 110.9% (104.4–116.6%) length, width across Ύ 107.1% (99.8–112.9%) length, width across Ɛ 111.6 % (105.0–115.7%) length, and width across posterior projections 128.4% (121.9–134.8%) length, sculpture somewhat effaced, but generally of semianastomosing ridges running subparallel to axis on fixigenae and more anastomosing ridges on glabella, scrobiculate where curving around anterior end of glabella; anterior branch of facial suture long, moderately laterally bowed, curvature strongest at mid-length of course along fixigena, more gently bowed anteriorly along exsagittal ends of anterior border; posterior branch of facial suture short (oblique), runs only along very short posterior fixigena and posterior border; anterior border short to very short, longest anterior to anterolateral corners of glabella, shorter sagittally and strongly tapered exsagittally, moderately inflated, anterior margin strongly anteriorly bowed, particularly medially, ventral margin forms very shallow “M”-shape (anterior view), sculpture of a few fine ridges near margin, running parallel to it; doublure only a rim ventrally, mainly expressed as median anterior face, very short, with a few transverse ridges; anterior border furrow short, fairly deep, with sharper contact anteriorly with border than posteriorly with frontal areas, shortest and most distinct just exsagittal to glabella, less distinct medially on all but largest specimen (Pl. 17, fig. 1), longer and shallower, grading posteriorly toward glabella, leading into very short, deeper preglabellar furrow observable on some specimens (e.g., Pl. 16, fig. 3, Pl. 17, fig. 10), course broadly anteriorly bowed, more strongly bowed around anterior of glabella where overlying preglabellar furrow on most specimens; glabella elongate, anteriorly tapered, bullet-shaped, with maximum width across L2 75.2% (72.1–79.9%) sagittal length, moderately vaulted (sag., tr.), with vaulting decreasing anterior to ocular ridge and far posteriorly over L1, with distinct L1 but other lobes unclearly defined, glabellar sculpture of fine, semi-anastomosing ridges running subparallel to axis for most of length, and strongly curved to match anterior curvature of glabella, with small, fairly widely spaced tubercles concentrated posteromedially, and with fine scrobiculate ridge on anteromedian rim of L1; L1 moderately independently inflated, strongly anterolaterally directed, short adaxially, lengthened abaxially, wide; S1 disconnected from axial furrows by very narrow strip of inflated glabella running from front of L1 to L2, moderately long, longer posteromedially, somewhat shorter anterolaterally, deep, deepest at anterolateral end; L2 poorly defined by either furrows or inflation, extremely short near axial furrows, very long medially; S2 expressed as extremely narrow and fairly short deep point just inside axial furrows midway between end of eye ridge and S1 (best observed on Pl. 17, fig. 10); L3 likewise poorly defined, very short and narrow, anteromedially directed; S3 deep, fairly short, very strongly anteromedially directed, located along sagittal end of eye ridge; LF extremely large, nearly half length of entire glabella, strongly anteriorly tapered; SO long and moderately deep, deeper laterally toward axial furrows, but effaced just adjacent to axial furrows, with transverse anterior margin and "W"-shaped posterior margin, ridge sculpture of glabella carries through SO to LO; LO moderately inflated, long medially, slightly shorter laterally, 16.4% (14.8–17.6%) sagittal length of cranidium, broad, with width across junction of axial furrows and posterior margin of cranidium 53.7% (49.9–57.9%) sagittal length of cranidium, lobe with shallowly "W"-shaped anterior margin, and with sculpture of very small, fairly widely spaced tubercles, line of tubercles along posterior edge, and with slightly larger median node located slightly anterior to mid-length, tubercles overlie fine, anteromedially angled semi-anastomosing ridges; doublure long medially, short and pinched out far exsagittally, with shallowly "W"-shaped anterior margin, and with sculpture of very fine, very closely spaced transverse ridges; axial furrows fairly shallow and narrow, wider and deeper along midlength of L1, across from posterior part of median end of ocular ridge (but effaced over anteriormost part of ridge), and along LF, course very slightly waisted along L1, gently laterally bowed around L2, then strongly anteriorly convergent; frontal areas trapezoidal, long and broad, with strongly posterolaterally sloped anterior and posterior margins, moderately anteroventrally sloped and gently anteriorly bowed (lateral view), with anastomosing ridge sculpture directed posteromedially anterior to fine scrobiculate ridge extending from a little posterior and exsagittal to junction of axial and anterior border furrows to β, ridges then directed more posteriorly, slightly laterally bowed posterior to scrobiculate ridge, frontal areas also with small raised bump near anteromedian end of ocular ridge indicating fossula for hypostome (visible ventrally, Pl. 17, fig. 12); ocular ridge relatively long, moderately inflated, posterolaterally directed at about 30º below horizontal, with moderately short, shallow furrows along anterior and posterior margins; palpebral furrow shallow, broad (long at anterior and posterior tips), very strongly laterally bowed, confluent with furrow along posterior margin of ocular ridge; palpebral lobes located far posteriorly on cranidium, across from L1, slightly anteroventrally and ventromedially sloped, small relative to cranidium overall, a little larger than semicircular in area, but closer to half-teardrop shaped, with anterior end of lobe extending slightly further adaxially and lobe more strongly curved posteriorly, with broad, slightly inflated lateral margin, margin broadest a little posterior to midlength of lobe; interocular fixigena trapezoidal, broad and fairly long, with strongly posterolaterally sloped anterior margin defined by ocular ridge, fixigena held nearly horizontally (anterior, lateral views), with weakly swollen crescentic rim outlining weakly depressed ala adjacent to L1; posterior fixigena relatively broad, very short, only a strip along anterior edge of posterior border, with extremely short laterally tapered section along projection of border, fixigena strongly posteroventrally downturned, with sculpture like that of frontal areas (continuous over entire fixigena); posterior border furrow short, very shallow and almost effaced adaxially, longer and deeper abaxially, then abruptly shallowed far abaxially along tips of posterior projections, course roughly transverse; posterior border narrow, short, slightly posteriorly lengthened along and just adaxial to posterior projections, moderately inflated, effaced, with short, very shallow furrow along posterior margin of projection for thoracic articulation (best seen on specimens of Pl. 17, figs 2, 17); doublure extremely short, only a rim until expanded into short wedge far exsagittally, effaced.

Hypostome unknown.

Librigenal measurements were made on the specimens of Pl. 18. Librigena of narrow, relatively elongate main body and very long genal spine; anterior branch of facial suture long (oblique), section along librigenal field slightly shorter than that along anterior projection of lateral border, suture forms smooth obtuse angle of about 120º at border, section along anterior projection of border cuts border, exposing wedge of inner surface; posterior branch of facial suture extremely short, only crosses posterior border, steeply sloped, with tiny recurved hook on posterior end to fit with posterior projection of cranidium; visual surface strongly convex, large, long and wide, reniform, composed of numerous tightly packed lenses, lenses smaller and less distinctly defined toward bottom of eye (Pl. 18, fig. 9); circumocular furrow narrow, deep (deeper posteriorly; shallower overall in larger specimens), more strongly curved anteriorly, intersects posterior border furrow approximately even with intersection of opposite end with anterior branch of facial suture; librigenal field trapezoidal, narrow (longer anteriorly and posteriorly) and relatively long, with minimum width under midpoint of eye 22.2% (18.9–27.7%) exsagittal length along lateral border furrow, field weakly laterally convex (exsag., tr.), with sculpture of narrow, scrobiculate ridge running in shallow arc from junction of circumocular and posterior border furrows anterolaterally to approximately mid-width of field along anterior branch of facial suture (joins ridge on frontal area of cranidium), and with fine anastomosing ridge sculpture feeding into scrobiculate ridge; sculpture abaxial to ridge directed anteromedially and sculpture adaxial to ridge directed anterolaterally (seen well on Pl. 18, fig. 8); lateral border furrow narrow and deep, course almost straight, only very slightly laterally bowed, furrow appears almost pitted in larger specimens (e.g., Pl. 18, fig. 2), separated from posterior border furrow by raised extension of base of genal spine running onto librigenal field; lateral border with sculpture near border furrow of fine, semi-anastomosing ridges directed posteromedially, effaced at mid-width, and with slightly thicker ridges parallel to arc of margin abaxially (these continue into spine sculpture), border moderately inflated, dorsoventrally flattened, bladed, with wedge-shaped cross-section, relatively broad, almost same width as narrowest part of librigenal field except in largest specimens, narrower along long anterior projection, with external side cut by facial suture and strongly anteriorly tapered down to point not quite at tip of projection, border merges posteriorly into genal spine; genal spine with short, semicylindrical, inflated base extending from genal angle anteromedially to a little less than half-width of field, main part of spine flattened and bladed similar to lateral border, very long, none complete, but at least 184.8% length of main body of librigena (Pl. 18, fig. 1), slightly broader than lateral border at genal angle, gradually tapered, smoothly and gently posteromedially curved, with sculpture of fine ridges forming herringbone chevrons, vertices of chevrons located near abaxial margin of spine and point anteriorly, sculpture continues on internal side of spine as other diagonal of chevrons; posterior border furrow short and deep, very incised where overlapped with circumocular furrow, shallower over border, course straight along field, then curved to cut across border at raised base of genal spine; posterior border similar to lateral border, but about 2/3 as long as width of former (shorter adaxially) and slightly more inflated, mostly effaced, with a few anastomosing ridges near furrow and a few linear ridges on posterior margin; doublure of posterior border long at genal angle, tapered sagittally to about half length of border, flattened (slopes anteriorly) and effaced, with shallow Panderian notch expressed mainly as indented anterior margin a little exsagittal of ω; lateral border doublure broad, just slightly narrower than border, of even width until tip of anterior projection, where cut by diagonal suture, doublure moderately inflated, with inflation highest just exsagittal from mid-width, with sculpture of fine ridges parallel to margin.

Measurements of thoracic segments were made on the specimens of Pl. 16 and were doubled as necessary for broken axial rings and pleurae. Total number of thoracic segments unknown; segments short and relatively broad, axis very broad, 46.4% (45.4–47.3%) total width of segment, moderately vaulted, more from axis than pleurae; articulating half ring lens-shaped, long medially and pinched out laterally, inset into axial ring such that anterior margin of segment is almost transverse, with only slight anterior bowing across half ring, with anastomosing line sculpture subparallel to sagittal axis on posterior portion (connected to furrow and axial ring sculpture), anterior part of ring effaced; articulating furrow fairly long and shallow medially, deeper and shorter laterally along taper of half ring, broadly posteriorly bowed, with line sculpture from axial ring extending into furrow; axial ring broad and relatively short, very slightly narrower posteriorly, moderately inflated, a little higher posteriorly, moderately dorsally arched, with sculpture of roughly transverse to posterolaterally directed anastomosing ridges and with small, flattened tubercles concentrated medially; doublure forms large articulating surface, roughly crescentic in shape, longest medially and strongly laterally tapered, effaced; axial furrows narrow, shallow anteriorly, much deeper posteriorly, approximately parallel-sided; inner pleurae horizontal, a little wider than outer pleurae; outer pleurae narrow, ventrolaterally sloped from fulcral angle of about 135º; anterior and posterior pleural bands about equal in length, anterior band a little shorter, particularly adaxially, with triangular (longer exsagittally) articulating wedge along outer pleurae; pleural furrow fairly long and shallow, a little deeper at fulcrum; posterior pleural band lengthened adaxially compared to anterior band, posterior margin transverse along inner pleurae and posteriorly bowed along outer pleurae; both bands nearly effaced, merged into spine at end of outer pleurae; spine incompletely preserved, roughly triangular, moderately wide, a little shorter than pleurae, base centered at about midlength of pleurae, with fine anastomosing ridges running along margins; doublure extremely narrow, just a rim curled in dorsomedially from base of pleural spine.

Pygidial measurements were taken from the specimens of Pl. 19 excluding the smallest specimen (Pl., 19, fig. 28). Measurements were doubled from the sagittal line if necessary, e.g., for specimens with only one side of the pleurae fully preserved. Pygidium composed of five segments with pleurae, plus additional two poorly expressed axial rings, moderately strongly vaulted (sag., tr.), lower posteriorly, very broad and fairly long, with width across first segment (excluding pleural spines) 143.3% (138.6–148.5%) sagittal length (excluding articulating half ring and furrow); articulating half ring broad and relatively short, 9.1% (8.5, 9.7%) sagittal length of pygidium, mostly effaced, with a little anastomosing ridge sculpture posteriorly; articulating furrow deep, long medially and shorter laterally, with transverse anterior margin and posteriorly bowed posterior margin; axis very long, almost equal to sagittal length of pygidium (94.6 [87.9–98.2%] length), wide anteriorly, with width of first axial ring 46.6% (44.9– 48.8%) width across first segment, strongly posteriorly tapered, with width across fourth axial ring 72.4% (71.3– 73.4%) width across first ring, strongly vaulted anteriorly, lower posteriorly; anterior two axial rings well independently inflated, posterior rings less inflated, with fifth ring only slightly raised above ring furrows, rings six and seven much less distinct, poorly independently inflated, mainly indicated by arrangement of weak inter-ring furrows and tuberculate sculpture, all rings short, particularly medially, with medially concave anterior margins and very slightly anteriorly bowed posterior margins on rings 1–4, all rings relatively broad, with sculpture of small tubercles concentrated medially, flanked by fine anastomosing ridges running subparallel to sagittal axis, and increasingly anteromedially directed on more anterior rings; inter-ring furrows long medially, likely include small pseudo-articulating half rings on at least segments 2–4, short near axial furrows, deep, particularly exsagittally, furrows 4–7 increasingly short and shallow (best visible on Pl. 19, fig. 3), course generally transverse, but exsagittal ends gently posterolaterally curved, sculpture of axis-subparallel anastomosing ridges carries through furrows from axial rings, median part of furrows more effaced, with a few granules posteriorly; rear of axis poorly defined (best seen on Pl. 19, fig. 3), a little shorter than wide, moderately convex (sag., tr.), with posterior margin steeply sloped down toward posteromedian spine, with sculpture similar to axial rings, except anteromedian anastomosing ridges wrap around posterior margin and more posterolateral ridges continue posteriorly onto spine; axial furrows mostly moderately narrow and deep, shallower along posterior rings and posterior of axis, strongly anteriorly divergent in course, posterior tips curve inward slightly to meet poorly expressed post-axial furrow, also abruptly shallowed anteriorly along first axial ring; inner pleurae broad and transverse, separated from steeply sloping outer pleurae of nearly equal width by fulcral angle of about 130º (Pl. 19, fig. 12), pleurae mostly effaced, with just sparse, faint, axis-subparallel anastomosing ridge sculpture sagittally on some specimens, and stronger ridge sculpture on short, posteriorly tapered, unfurrowed pleural region adjacent to posterior of axis; anterior pleural bands very slightly independently inflated, a little longer abaxially than adaxially, posterolaterally directed, with fairly large triangular articulating facet on outer pleurae of first segment; pleural furrows long and deep, shallower just adjacent to axial furrows (distinctly so in larger specimens), proportionately shorter posteriorly, posterolaterally directed, increasingly so posteriorly; posterior pleural bands similar to anterior bands, but longer adaxially than abaxially; interpleural furrows moderately short, very shallow, very nearly effaced in some specimens, similar in course to pleural furrows but a little more laterally and less posteriorly angled; pleural spines produced from just above base of outer pleurae, extend posterolateroventrally, with posterior spines increasingly posteriorly directed (fourth pair subparallel, fifth pair posteromedially directed), long at base and strongly tapered to sharp point, a little narrower than corresponding pleural band, with sculpture of anastomosing ridges roughly following contours of spine on dorsal aspect, ridges more widely spaced than those on main body of pygidium, with some sculpture at base of spines extending onto outer pleurae, mostly effaced ventrally; posteromedian spine moderately long, with free length 50.3% sagittal length of pygidium (Pl. 19, fig. 1), robustly conical, with fairly broad base separated from axis by distinct break in slope and moderately long, shallow post-axial furrow, spine posteriorly tapered to blunt point, held roughly horizontally, or slightly posterodorsally directed, with concentric sculpture of fine ridges forming inverted “V”-shapes dorsally and “V”-shapes ventrally, with some anastomosing ridge segments; pygidial border mainly expressed ventrally, partially visible as posterior margin of pygidium from fifth pleural spine pair back to underneath base of posteromedian spine, moderately inflated, extends vertically beneath bases of pleural spines on sides of pygidium, then rises up posteriorly to merge with pleural region into base of posteromedian spine, with sculpture of concentric ridges a little coarser than those of pygidial axis following shape of border; doublure only visible in anterior view (Pl. 19, fig. 12), held roughly vertically, shallowly "W"-shaped, longest medially over rounded dorsal extension into hollow at base of posteromedian spine, then anterolaterally tapered, with sculpture of subparallel fine ridges following shape of margin.

Ontogeny. Cranidia of P. acicaudus (cf. Pl. 16, fig. 2 and Pl. 17, figs 1, 10) broaden overall; the anterior border shortens, particularly medially, as does the anterior border furrow, although the furrow appears to lengthen initially before shortening again (cf. Pl. 16 figs 2 vs 1, 3 and Pl. 17, figs 1–3); the glabella inflates and becomes more vaulted (sag.; transverse convexity remains similar), broader, and its sparse tuberculate sculpture effaces, particularly anteriorly; L1 becomes longer and larger; SO lengthens and shallows medially; LO shortens, inflates, and the tubercles become less prominent; the lateral margins of the frontal area (anterior branch of the facial suture) become less laterally bowed and straighter; the fixigenal boss above the fossula becomes more prominent; the eye ridge inflates; the palpebral lobes become smaller (both shorter and narrower) relative to rest of cranidium; and the posterior fixigena narrows relative to the glabella.

Librigenal changes (cf. Pl. 18, figs 2, 15) include shallowing of the circumocular furrow, significant widening of the librigenal field, stronger expression of the scrobiculate line sculpture on the field, stronger inflation and further adaxial extent of the base of the genal spine on the field, widening/lengthening of the lateral and posterior border furrows, and effacement of the linear and herringbone chevron sculpture of the lateral border and genal spine.

Thoracic segments are insufficiently known for discussion of ontogeny.

Pygidia (cf. Pl. 19, figs 1, 22, 28) become relatively narrower and more elongate; the anterior and posterior margins of the first axial ring curve toward each other with increasing expression of pseudoarticulating half ring and shorten axial ring medially; tuberculation develops on axis, and anastomosing line sculpture on axis, pleurae, and margin strengthens; the pleural furrows deepen slightly; and the posteromedian spine shortens and thickens.

Discussion. Hintze's (1953, pl. 27, figs 9, 10) holotype pygidium and an associated cranidium came from surface specimens at Section CP 45.7 m. All of the material illustrated herein came from a small, highly fossiliferous limestone nodule collected in situ in shale at CP 48.8 m. The fauna is overwhelmingly dominated by P. acicaudus , but also contains rare sclerites of the associated species documented by Hintze (1953).

Resolution of relationships between the most derived four species of Pseudoolenoides is the least well supported region of the tree. Pseudoolenoides acicaudus is very similar to P. oilcreekensis (which Shaw (1974) identified as P. acicaudus ) and differences between these species are discussed below. It is also quite similar in many details to P. fossilmountainensis . Pseudoolenoides acicaudus is the only species which retains five unreleased thoracic segments, which differentiates it from all other species. In cranidial features, it differs from P. fossilmountainensis in a complete lack of glabellar tubercles versus a medially concentrated scattering of small tubercles, less posteriorly bowed anterior sections of the facial suture, more anteroposteriorly oriented, less anastomosing, more widely spaced, and generally more subdued raised line sculpture, and distinctly smaller palpebral lobes. In anterior view, the palpebral lobes are less elevated and more nearly horizontal. Librigenae of the species are very similar, and share a small posterior point where the posterior border meets the facial suture, but that of P. acicaudus is larger and more prominent. The librigenal field is also narrower and the raised line arc less well expressed. The species are most different in their pygidial morphology. In addition to retaining an extra unreleased segment, the pygidium of P. acicaudus has a much broader posterior axis, axial furrows which converge posteriorly to a much lesser degree, and a relatively short, tapering posteromedian spine versus long and nontapering (at least proximally).